1. Field of the Invention
The present invention relates to a constant velocity joint boot and more particularly to a constant velocity joint boot which is placed to cover a constant velocity joint which is inevitable as a drive shaft joint for a front-wheel-drive vehicle.
2. Related Art
A joint portion of a constant velocity joint is covered by a bellows-shaped boot in which grease is sealed so as to prevent the intrusion of water and dust to thereby maintain smooth rotation at large angles. This constant velocity joint boot is made up of a larger cylindrical portion which is fastened to a joint outer race or the like, a smaller cylindrical portion that smaller in diameter than the larger cylindrical portion and which is fastened to a shaft and a bellows portion having substantially the shape of a frustum of triangular pyramid which connects the larger cylindrical portion and the smaller cylindrical portion together. Then, when in use, since the bellows portion deforms as an angle formed between the joint outer race or the like and the shaft (a joint angle) varies, even in the event that the angle increases, the joint portion can be sealed off by the boot in an ensured fashion.
Incidentally, in the event that the joint angles decreases and the bellows portion rotates at a small angle such as on the order of 20 degrees or smaller, there sometimes occurs a case where a stress exerted on the small cylindrical portion substantially equals a stress exerted on a root portion of the bellows portion. As this occurs, there sometimes occurs a risk that an early crack is generated in the smaller cylindrical portion at a portion thereof which lies near a boundary with the bellows portion. Note that when a bending angle of the bellows portion is large, a larger stress is exerted on the larger cylindrical portion than on the smaller cylindrical portion, whereby a crack is generated in the bellows portion. Due to this, there has been desired a constant velocity joint boot having such a durability that the generation of a crack in the smaller cylindrical portion can be suppressed, even in the event that the bellows portion bends at the small angle of on the order of 20 degrees or smaller.
Then, JP-A-2003-329136 discloses a technique which suppresses the generation of a crack in the smaller cylindrical portion at the portion thereof which lies near the boundary with the bellows portion.
In this technique, as shown in FIG. 7, a shoulder portion 93 of a clamp groove (a groove on which a fastening member is fitted) 91 formed on an outer peripheral surface of a small cylindrical portion 90 which lies to face a bellows portion 92 is cut away along the full circumference thereof, whereby a circumferentially extending cut-away portion 94 is formed on the shoulder portion 93. Then, it is mentioned in the technique that since the volume of the shoulder portion 93 can e reduced by virtue of the existence of the cut-away portion 94 like this, a stress exerted on an end portion of the clamp groove 91 which lies to face the bellows portion 92 can be relaxed, the durability of a boot can be increased.
Even with the aforesaid conventional constant velocity joint boot, however, the generation of a crack in the smaller cylindrical portion due to the stress exerted when the bellows portion bends at small angles cannot necessarily be suppressed in a sufficient manner.